Surgical staplers have been used in the prior art to simultaneously make a longitudinal incision in tissue and apply lines of staples on opposing sides of the incision. Such instruments commonly include a pair of cooperating jaw members that, if the instrument is intended for endoscopic or laparoscopic applications, are capable of passing through a cannula passageway. One of the jaw members receives a staple cartridge having at least two laterally spaced rows of staples. The other jaw member defines an anvil having staple-forming pockets aligned with the rows of staples in the cartridge. The instrument includes a plurality of reciprocating wedges which, when driven distally, pass through openings in the staple cartridge and engage drivers supporting the staples to effect the firing of the staples toward the anvil.
An example of a surgical stapler suitable for endoscopic applications is described in U.S. Pat. No. 5,465,895, which advantageously provides distinct closing and firing actions. Thereby, a clinician is able to close the jaw members upon tissue to position the tissue prior to firing. Once the clinician has determined that the jaw members are properly gripping tissue, the clinician can then fire the surgical stapler, thereby severing and stapling the tissue. The simultaneous severing and stapling avoids complications that may arise when performing such actions sequentially with different surgical tools that respectively only sever or staple.
One specific advantage of being able to close upon tissue before firing is that the clinician is able to verify via an endoscope that a sufficient amount of tissue has been captured between opposing jaws. Otherwise, opposing jaws may be drawn too close together, especially pinching at their distal ends, and thus not effectively forming closed staples in the severed tissue. Moreover, a firing bar that traverses between opposing jaws to sever the tissue and to drive the wedges that drive the staples may encounter resistance due to the pinched opposing jaws. At the other extreme, clamping upon too much tissue may create similar problems. The cutting edge may incompletely sever the tissue and/or the staples may not fully form. Relying upon endoscopic verification of proper clamping may be undesirable or ineffective in all instances to detect when too much or too little tissue has been clamped.
Thus, while such surgical staplers have been a significant advance in surgical procedures, an opportunity has been recognized for enhancing their effectiveness. In particular, it would be desirable to affirmatively maintain proper spacing between the opposing jaws during firing and to prevent entirely severing and stapling unless the thickness is appropriate for ensuring an effective operation.
Consequently, a significant need exists for an improved surgical stapling and severing instrument that maintains proper spacing in its end effector to achieve proper stapling of the severed tissue that prevents firing (i.e., severing and stapling) when the opposing jaws are not closed.